Rotary, push-pull switches have received widespread use within the automobile industry. This type of combination switch is typically used to operate the headlights by utilizing the push-pull action of the switch and to control the intensity of the dashboard panel lights by utilizing the rotary action of the switch to operate a rheostat. In addition, attempts have been made to utilize the rotary action to control supplemental electrical circuits, such as a dome light bypass switch (to prevent door switches from energizing the dome light).
The use of these combination switches as headlight switches in automobiles puts several limitations on the design of the switch. The first is a need for compactness due to the confined space in which the headlight switch is located, which is typically on the dashboard to the left of the steering wheel. Second, the headlight switch must be uniform in size and design in order to fit within a wide variety of automobiles. Finally, there is a need for ease of fabrication and for minimal fabrication costs due to the large quantities of headlight switches produced.
The prior art contains several attempts to produce a combination switch with a supplemental switch to control the dome light bypass circuit and which meets the requirements for use as an automotive headlight switch. One such switch utilizes a rotating rheostat with a projection which engages a dome light bypass switch externally mounted on the side of the headlight switch housing. The dome light bypass switch consists of an exposed arm extending longitudinally up the side and parallel to the shaft. This switch is limited in applicability due to increased size, susceptibility to damage due to exposure of the external arm, and sensitivity to tolerance accumulation during fabrication of the switch.
In U.S. Pat. No. 4,885,434, a headlight switch with rotating arms mounted on the shaft and a stationary rheostat is described. A dome light bypass switch is internal to the headlight switch housing and functions by having one of the rotating arms engage a plunger which pushes open the dome light bypass switch. The plunger and dome light bypass switch are disposed on the stationary rheostat. Although this headlight switch solves the problems related to the size of such switches, it is difficult to fabricate due to the use of several leaf-type contacts which require extraordinary care during fabrication in order to prevent damage.
An alternative solution is suggested in U.S. Pat. No. 4,827,241 which utilizes a projection on a driver assembly to engage a dome light bypass switch which is sandwiched in line with the rotating components. As with the previous headlight switch, the dome light bypass switch is internal to the headlight switch housing, which results in a compact switch. In addition, this headlight switch is very forgiving to tolerance accumulation during fabrication. Unfortunately, the rotational components have to be small due to the sandwich arrangement and this leads to an overheating problem which limits the switch to low current applications (less than 5 Amp). The low current limitation makes this switch inadequate for the desired automotive use.